Recently, it has been shown that the immunohistochemical loss of BAF47 reactivity identifies the vast majority of AT/RTs.
We also assessed the utility of reticulin staining and immunohistochemical reactions for OTX2 and BAF47 as objective standards for predicting PFS and OS.
The data also support the routine use of BAF47 immunoreactivity in analyzing small cell embryonal tumors, the use of OTX2 to characterize anaplasia in MBs, the identification of moderate to severe anaplasia in MBs, and the recognition of nodularity in MBs, all of which proved significant in characterizing prognosis in embryonal tumors of the pediatric CNS.
For the slides to be tested for BAF47 expression, the slides were placed in preheated Tris/EDTA, pH 9.
As a result of the previous studies of Haberler et al, (21) BAF47 immunohistochemistry was performed on 32 tumors for which at least 1 pathologist made a diagnosis of MB; BAF47 reactivity was diffuse in 17 cases, multifocal in 14 cases, and absent in 1 case.
To compare the immunoreactivity of BAF47 in these tumors versus the AT/RTs, a sample of 6 AT/RTs as diagnosed by the originating institution were analyzed for BAF47 expression; BAF47 was absent in 5 of 6 (Table 4).
The BAF47 antibody has proven its utility in objectively identifying the nonexpressing AT/RTs from other expressing tumors in the differential diagnosis with rare exception.
The literature has indicated that the otherwise typical-appearing MBs with diffuse histology, but negative expression of BAF47, all proved to have poor clinical outcomes, and were best considered AT/RTs.